Aldoheptose Biosynthesis. Previously, a novobiocin-hypersensitive mutant of Escherichia coli K-12 carrying a cysE-pyrE linked mutation, designated rfaD, which specifically affects the synthesis of the aldoheptose, L-glycero-D-mannoheptose, has been isolated and genetically characterized. The rfaD gene codes for ADP-L-glycero-D-Mannoheptose-6-epimerase, an enzyme required for lipopolysaccharide (LPS) core biosynthesis. The nucleotide ADP-D-glycero-D-mannoheptose accumulates in rfaD mutant strains. The rfaD phenotype includes increased permeability to a large number of hydrophobic antibiotics, and the formation of mucoid colonies. A 9-kilo-base DNA EcoRI fragment carrying the rfaD gene was initially identified in the Clarke-Carbon Colony Bank cloned in pBR322, and subsequently smaller restriction fragments were cloned into several expression plasmid vectors. RfaD+ plasmids express a protein with a molecular weight of 37,000, and all complement all phenotypes associated with the rfad mutation. Finally ADP-L-glycero-D- mannoheptose-6-epimerase has been purified to homogeneity. Hepatitis Non-A, Non-B. Hepatitis non-A, non-B (HNANB) is a world-wide problem, and 90% of the transfusion-related hepatitis cases in the United States (and 80-90% in several other countries) are diagnosed (by exclusion) as HNANB. Approximately 50% of all acute HNANB patients develop chronic HNANB (an estimate of 4 million persons). Biochemical, immunological, and morphological evidence suggested that the HNANB agent is a mammalian type C retrovirus. Recently, using an in vitro focus-induction assay developed for mammalian type C viruses, we observed that pelleted material from HNANB sera (transfusion-related) induced foci formation. A DNA probe of 780 base pairs isolated from HNANB-infected chimpanzee liver and selected by subtractive hybridization with normal chimpanzee liver was shown to hybridize with liver sections from three HNANB-infected chimpanzees but not with liver from two HBV-infected animals. This DNA fragment has been cloned, completely sequenced, and placed under the control of the Sp6 promoter.